The structure, replication, and interactions with cell membranes of myxoviruses and paramyxoviruses will be studied using influenza virus and the parainfluenza virus SV5 as models. These studies are designated not only to gain knowledge of these viruses and their mechanisms of pathogenesis, but also to provide information regarding cell membrane structure and biogenesis. The goals are to define the structure and composition of these viruses and correlate the various biological activities of the virion with specific viral components, to explore the biosynthesis of viral macromolecules in infected cells, and to determine the sequence of events in the incorporation of viral proteins into the cell membrane and the assembly of the virion. The mechanism of virus- induced cell fusion, and the effects of membrane lipid composition of this reaction will be investigated. Paramyxoviruses have been implicated in the etiology of several chronic diseases, and these viruses also induce persistent infection in cell culture. Viral and cellular macromolecular synthesis will be investigated in cells persistently infected with SV5 with the aim of elucidating the mechanisms involved in the control of persistent infection and the long-term effect of such infection on cells. The production of incomplete and defective influenza and SV5 virus particles in various cell types will be investigated to determine the effects of these particles on the host cell and the course of virus infection. Biological and biochemical studies of the viruses, viral components, and virus-infected cells will be correlated with electron microscopic studies.